Biochemical Profiling of Phenolic Compounds in Lentil Seeds

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Date

2016-09-21

Author

Mirali, Mahla

Type

Thesis

Degree Level

Doctoral

Abstract

Lentil (Lens culinaris Medikus) is an annual cool-season legume with a variety of seed
coat colours. Seed coat colour is an important grading factor that affects the market
value of lentils. In lentil, two independent loci gray ground colour (Ggc) and tan ground
colour (Tgc) determine the four basic seed coat background colours; brown (Ggc Tgc),
gray (Ggc tgc), tan (ggc Tgc) and green (ggc tgc). The zero tannin locus (tan) is
epistatic to the tgc locus, producing clear seed coats. Lentil is a good source of protein,
carbohydrates, dietary fiber components, minerals, vitamins, and secondary metabolites
that include phenolic compounds. Phenolic compounds produce different pigments in
plants and bring health benefits to humans. The overall objective of this study was to
determine the relationship between seed coat colour and phenolic compounds in lentil.
In the first study, comparison of the phenolic profiles of four seed coat background
colours in lentil (i.e., brown, gray, tan, and green) was performed using an optimized
liquid chromatography-mass spectrometry (LC-MS) method. The results showed that for
the levels of various phenolic compounds in lentil seeds varied with the seed coat
colour. Specifically, seed coats of lentil genotypes carrying the homozygous recessive
tgc allele (green and gray seed coats) had higher amounts of flavan-3-ols,
proanthocyanidins, and some flavonols.
In the second study, a comparison was made between the phenolic profiles of lentil
seed coats that do not express the Tgc phenotype (genotype Tgc tan) and those that
express Tgc (genotype Tgc Tan). The LC-MS analysis detected several compounds that were not influenced by tan, notably the phenolic acids, flavones, some flavonols,
and some of dihydroflavonols. In contrast, myricetin, dihydromyricetin, and flavan-3-ols,
and proanthocyanidin oligomers were detected only in Ggc Tgc Tan lines and therefore
appear to be controlled by tan. The molecular analysis showed that tan is a basic-helixloop-
helix (bHLH) transcription factor that could interact with the regulatory genes in the
phenylpropanoid pathway for the enzymes flavonoid-3’,5’-hydroxylase (F3’5’H) and
dihydroflavonol reductase (DFR).
The third study measured the effect of long term storage on specific changes in
phenolic compounds in lentil seeds. Increases in phenolic acids and flavones occur in
green lentil seeds during storage, possibly because of the breakdown of more complex
species into smaller subunits. More interestingly, a significant decrease in 27 flavan-3-
ols and proanthocyanidins also occurs. Polymerization of flavan-3-ols and
proanthocyanidins and their conjugation to cellular constituents could reduce their
extractability and produce dark pigments in long stored lentil seeds.
In conclusion, these studies determined that there is a relationship between phenolic
compounds, specifically flavan-3-ols and proanthocyanidins, and seed coat colour
genes tgc and tan in lentil. The findings of this study will help to develop future breeding
strategies for lentil cultivars with aesthetic properties and nutritional benefits that appeal
to consumers.